Ferroelectric domain shifting devices

ABSTRACT

Ferroelectric crystals which are also ferroelastic, such as gadolinium molybdate, can support stable internal ferroelectric polarization domains. These domains are expanded and moved in the ferroelectric crystal by means of a sequence of voltages applied to electrodes on the surface of the crystal. Thereby, optically readable, shift register logic functions are achieved using (for readout) an incident optical beam with respect to which the ferroelectric domains are birefringent.

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[4 1 Get. 24-, 11972 References Cited FERROELECTREQ DOMAIN SHHFTIING [56] DEVKCES UNITED STATES PATENTS [72] Inventors: Joseph Edward Geusic, Berkeley Heights. Terence 36h Nelsen, New 3,229,261 1/1966 Fatuazo ..340/ 173.2 Providence; David PW} gamma! 3,362,019 1/1968 Gratianm' ..340/l73.2 Berkeley Helghts an of Primary Examiner-Terell W. Fears [73] Assignee: Bel Teieyhone Laborainriw, Hncor- Attorney-11. J. Guenther et al.

porated, Murray Hill, N]. H 22 Filed: Aug. 25, 11971 [57] ABS CT 7 Ferroelectric crystals which are also ferroelastic, such APPL 1749727 as gadol ir iigrg glve l are can support stable internal fefioelectric polarization domains. These domains are expmded and moved in the ferroelectric crystal by means of a sequence of voltages applied to electrodes [52] 10.5. C1. "340/1732, 340/173 LS on the surface of the crystaL Thereby, Optically reada [51] 131i. Cl. Gilt! 11/22 ble, Shift register logic functions are achieved using Fleid 0? Search (for readout) an incident optical beam with respect to which the ferroelectric domains are birefringent.

11) Claims, 6 Drawing Figures OPTICAL DETECTOR AND UTlLlZATlON MEANS 460 ANALYZER\l l l l l l l l l 1 M56 c I 155 lilillliilllillll/w I l 1 l 1 7 1 2 3 4 5 6 7 e LCQ 1 T -i' --2 w H @5 8 a} 2/ E [El 122 I23 I24 I26 127 2 IBO "i 132 l33 I34 135 l36 l37 138 we .1: T T SOURCE j ]43 QUARTER WAVE. PLATE l 153 H52 iilliiliiliiiilil ei OPTICAL SOURCE FERROELECTRIC DOMAEQ S l 1 l .l' G DEVHCES HELD OF THE INVENTION This invention relates to electrooptical information handling and display systems, and more particularly to ferroelectric optical devices.

BACKGROUND OF THE INVENTION In US. Pat. No. 3,142,045, issued to A. H. Bobeck on July 21, 1964, there is described a shift register device using a ferroelectric crystal as the memory propagating medium, which can support two states of information in the form of domains of internal electric polarization. Information address (creation) of each domain followed by shifting propagation of the domain, as well as subsequent creation of a new domain, was accomplished by means of a six-phase voltage pulse source circuit. The six-phase characteristic of the voltage pulse circuit was necessitated by the use therein of information bit groups each comprising a plurality of electrode segments. On the other hand, it is known that those ferroelectric crystals which are also ferroelastic can support domains of internal polarization which are more stable than domains in ferroelectric crystals which are not ferroelastic.

SUMMARY OF THE INVENTION We have found that an information bit (polarization domain) in a ferroelectric crystal, which is advantageously also ferroelastic, can be defined by a single electrode segment, thereby enabling the use of simpler domain propagation (shifting) circuits than in the prior art. Specifically, using ferroelectric crystals which can support domains of polarization, and advantageously which are also ferroelastic, a three-phase voltage pulse circuit is utilized in a ferroelectric polarization domain shifting device. As used herein, the term domain means a region of one internal ferroelectric polarization direction in the crystal surrounded by region(s) of different (typically opposite) internal polarization and by the physical boundary of the crystal itself (only partially, if at all). Each bit location is defined by a single electrode to which voltage pulses are applied. Information is contained in the pattern of domains of polarization in the crystal, each domain being in one of two stable states of internal electric polarization. Readout of the pattern of domains at any instant can be accomplished with a polarized optical beam, since the optical birefringence of the crystal is a function of the state'of polarization. Thus, shifting optical display devices, as well as shift register logic function devices, can be provided using the principles of this invention.

In a specific embodiment of the invention, a ferroelectric crystal of gadolinium molybdate serves as the information propagating medium. A three-phase voltage pulse circuit is connected to an array of electrodes on a major surface of the crystal, in order to furnish electric fields in the crystal which create and propagate information 'in the crystal in the form of internal polarization domains in the crystal. Readout of the pattern of domains at any particular location (or over the whole operating portion of the crystal) is accomplished by means of a beam of light incident upon the crystal located between a quarter-wave plate and an optical polarizer and an analyzer.

In another specific embodiment of this invention, three essentially identical ferroelectric parallel-sided plates are arranged such that a beam of optical radiation passes through all of them. Domains of ferroelectric polarization in the plates are characterized by two states of polarization, corresponding in one state to a relative phase retardation between orthogonal polarizations in the beam equal to one-quarter of a wavelength of the optical radiation, and in the other state to a relative phase retardation also of one-quarter of a wavelength but in the opposite sense. By appropriate shifting of the domains in the three plates, in conjunction with a quarter-wave plate, a switching optical half-wave retardation device is formed. Such a device is useful, for example, in an optical shutter formed by locating the half-wave retardation device between a pair of crossed optical polarizers.

This invention, together with its objects, advantages, and features can be better understood from the following detailed description when read in conjunction with the drawing in which:

FIG. 1 is a side view diagram of ferroelectric shift register apparatus in accordance with a specific embodiment of the invention;

FIG. 2 is a top view diagram of the apparatus shown in FIG. ll;

HO. 3 is a plot of voltage versus time, useful in describing the operation of the apparatus shown in FIGS. l and 2;;

FIG. 4 is an illustrative diagram of a mode of ferroelectric domain propagation in the operation of the apparatus shown in FIGS. 1 and 2;

H6. 5 is a side view diagram of an optical shutter, in accordance with another specific embodiment of the invention; and

E6. 6 is a top view diagram of the apparatus shown in FIG. 5.

FIGS. 1 and 2 show a ferroelectric crystal plate 100 with a grounded transparent electrode layer ill) on a major surface thereof, and an array of transparent electrodes 326 128 on an opposed major surface. Typically, the plate fltlt) is a single crystal of gadolinium molybdate oriented with its 0 axis parallel to an incoming monochromatic beam 151i of optical radiation from an optical source 150, typically a helium-neon or other visible laser source. A polarizer 152 is oriented to transmit only that transverse optical polarization component of the beam 151 which is parallel to the x axis indicated at the left-hand side of FIG. 2, that is, at 45 with respect to the (orthogonal) a and b axes of the crystal plate 1%. In addition, a quarter-wave plate 153 retards the a-component of optical polarization of the incoming beam by a phase of with respect to the [7- component. The thickness of the plate itld is selected advantageously such that the aand b-components of the optical radiation are further and selectively (along the cross section of the beam) relatively retarded by i 90 upon propagating through the plate res, depending upon the state of electric polarization of the corresponding portions of the plate ltli) through which the optical beam propagates. Thereby, in propagating through both the quarter-wave plate 153 and the ferroelectric crystal Hill, the various portions of the cross section of the optical beam 154 (along the x direction) have undergone a total relative phase retardation between the a and b optical polarization components of advantageously or 180 depending upon the distribution (along the x direction) of the states of electric polarization (tc orientation) in the crystal ltl'll. These latter states depend upon the sequence of voltage pulscs applied to the electrodes i2-128, as described herein below. After propagating through an optical analyzer 155, which is crossed with respect to the polarizer N2, the exit beam 156 is impressed with a pattern of bright and dark portions along the x direction, because (as known in the art) a relau've phase retardation of 180 of orthogonal a and 1) optical polarization components corresponds to a rotation of the direction of polarization in space by 90. An optical detector and utilization means 166 detects and utilizes this exit beam 156.

in order to impress the shifting pattern of bright and dark portions upon the exit beam E56, a voltage pulse source 2.41% having three output terminals Ml, 1 142, and 143 provides voltage pulses, in sequence described below, to the electrodes 120-128, in accordance with the time sequence indicated in FIG. 3, by means of Wire leads 130433. it should be noted that advantageously one of the electrodes, the edge electrode 120, can be disconnected from terminal 141 by a switch on wire lead T130, in order to provide means for controlling the application vel non of any voltage pulses from the terminal full. to the electrode 120 and hence to control the initial write-in of a bit of information (polarization state) to the left-hand edge of the crystal lllll.

To operate the apparatus shown in LEGS. l and 2 as indicated in H6. 3, at time a positive voltage pulse is applied to the terminal 141 of the voltage pulse source 341'). At a later time, t a positive pulse is applied to the terminal 342, etc. Between t and a negative pulse is applied to the terminal 143, etc,

in order to explain the operation of the apparatus shown in FIGS. 1 and 2, reference is made to FIG. 4- in which ".e propagation of i domains (i.e., internally polarize the positive 0 direction) is shown in a time plot illustrating the position and extent of these positive" domains as time progresses. Assuming that the switch connecting the wire lead 33!} with the electrode 12% is closed when the pulse at 2 is applied, and assurning that initially the plate 1% is everywhere internally polarized in the negative 0 direction, then when the first positive pulse is applied at 1 from terminal 141 to the electrode 124), the plate filth) will be polarized in the positive c direction, as indicated in PEG. 3, from the left-hand edge to x x (that is, underneath electrode 12%) and in the negative 0 direction for x x Similarly, when the positivepulse at Z is applied to electrode 121, then the plate Elli? becomes polarized in the positive 0 direction from the left-hand edge to x =x (FIG. Ll), i.e., under electrodes ll2ti and 121i, and remains negatively polarized elsewhere. Then, as further indicated in FIG. 4, when a negative pulse from terminal M2 is applied to electrode 121 between times t and only that portion of the plate llltl underneath electrode 121i remains polarized in the positive 0 direction. As further illustrated in FlG. 4, when a posi* tive pulse is thereafter applied at time from terminal I143 to electrode 322, then the plate is polarized in the positive 0 direction under both the electrodes 121i and i223, and in tne negative c direction elsewhere in the plate. Thereafter, a negative pulse from terminal parallel to the positive c axis under electrodes 12%, 122,

' and 123, and parallel to the negative 0 axis elsewhere in the plate 0n the other hand, if during this last pulse at the switch on wire lead 13% had been kept open, the polarization in the plate under electrode 12% would have remained parallel to the negative c axis, thereby affording the capability of write-in vel non of a positive internal polarization to be shifted along the x direction. Thus, the sequence of pulses shown in FIG. 3, provides a three-phase applied pulse voltage for propagation of domains along the x direction of the plate res, as illustrated in FIG. 4 (assuming the switch on wire lead Iii-3t) is always closed), each domain being a local region of internal ferroelectric polarization parallel to the positive or to the negative 0 axis of this crystal plate Kilt).

Advantageously, the electrodes 129-123 (FIG. 2) all extend in the i y direction to the edges of the plate llltl, so that the domains likewise'extend in the i y direction to these edges. Thus, the boundaries of each domain in the xy plane will be coextensive with the projection of the outer contour of a single one of the electrodes or a group of next neighboring electrodes (FIG. 4).

it should be apparent that a plurality of plates similar to the plate ltlil can be juxtapositioned so as to provide a two-dimensional array of shifting domains suitable for shifting optical display systems.

in a typical example by way of illustration only, the plate ltltl is gadolinium molybdate, 0.033 cm thick in the c direction, and each of the electrodes l2tl-128 is 0.1 cm wide in the x direction and 0.2 cm in the y direction. (PEG. 2, left-hand side). Each of the voltage pulses supplied by the source l lll to the terminals Edi-i 33 is :t 200 volts with a pulse duration of 10' sec. The wavelength of the optical radiation in the beam 151 supplied by the source 15d is 6,328 angstroms (helium-neon laser).

it should be pointed out that it is advantageous that the end electrode 32 extend sufficiently close to the edge of the plate lull (or overlap same), in order that a pulse from terminal Ml will produce the edge domain corresponding to the polarity of the pulse, since the threshold for domain formation (as opposed to movernent of its boundary) is relatively much greater in the interior of the plate ltll) than at its edges. in addition, jtlre l hickness oithe plate res car be doubled, in order to furnish a l (instead of change in relative plla se reiirditidn b etween the a and b polarization components, at some sacrifice of further optical radiation loss in the plate but thereby obviating the need for the quarter-wave plate l53.

FIGS. 5 and 6 illustrate another embodiment of the invention, in which three ferroelectric plates 2%, 3th), and 4% are arranged as the electrooptic element of an optical shutter device. Each of the plates 2th), 381}, and ddil is similar to the plate ltltl described above including transparent grounded electrodes 21G, Elli), and 419, except that in FEGS. 5 and 6 transparent electrodes 221-228, 321-328, Qti223 are arranged (HG. ad-

vantageously much longer in the y direction than in the x direction, and only every third electrode is permanently connected to a voltage battery source dill through a single-pole double-throw switch 662. in addition, the ferroelectric polarization directions of domains in the plates 2%, 3%, and dill) in regions underneath the other electrodes, which are not connected to the switch 662, are permanently set in the directions indicated by the one-way arrows in FIG. 6. This can be accomplished, for example, by propagating these domains by means indicated above in the description of the apparatus shown in P768. 1 and 2.

On the other hand, the polarization direction in the plates 23 3th), and dill) in these regions underneath those electrodes which are connected to the switch 602 are switched in the i c direction alternately by reason of throwin g of the switch 6&2 to the positive or negative terminal of the battery dill. A voltage pulse source can obviously be used in place of the battery 6G1 and switch i502.

in operation of the apparatus shown in FIGS. 5 and 6, an optical source 569 provides a preferably monochromatic beam of light 5% which propagates through an optical polarizer $02. Advantageously, the polarizer 5G2 is oriented to polarize the beam in the x direction, i.e., at 45 to the (orthogonal) a and b axes of the crystal plates .260, Bill), and til-t) (all of which plates are aligned with their a and b axes mutually parallel). Then the beam of light propagates through a quarterwave plate 563 which retards the a component of optical radiation by a 90 phase shift more than the b component. Thereafter, the beam of light propagates through the plates 2%, 3%, and 4%, wherein the a and b components of optical radiation are relatively retarded advantageously by 90 in each plate, depending upon the direction of'ferroelectric polarization in the domains through which the various portions of the cross section of the beam of light propagate. Thus, on propagating through both the quarter-wave plate 563 and the plates 299, Bill), and dilh, the various portions of the cross section of the optical beam undergo a total relative phase retardation equal to 90 :t 90 O or 180", depending upon the throw of the switch s02; since each portion of the beam propagates through two plates of opposite direction of domain polarization thereby producing a zero net relative phase retardation, and through the quarter-wave plate 593 and a third plate 283), 3th), or Mill in which the polarization of the domain in the path of that portion of the beam can be in the i c direction, depending upon the position of the switch 6G2 (and hence the polarity of the voltage supplied by the battery 6%). As known in the art, a 180 relative phase retardation between orthogonal components of optical radiation corresponds to a spatial rotation of the direction of optical polarization equal to 90. Thus, the beam of light 51M], exiting from the plate d ll), which is incident upon the optical analyzer 595, advantageously crossed" (axis oriented perpendicular) with respect to the polarizer 5&2, will be extinguished or not, depending upon the throw of the switch 5137; that is, depending upon the polarity of the voltage supplied by the battery 41 6 to those electrodes on the plates 2%, 3%, add to which this battery is connected. Thereafter, the resulting beam of light 5% (to the extent it is not extinguished) exiting form the analyzer 505 is detected and utilized by the means 5% therefor.

Thus, the apparatus shown in FIGS. 5 and 6 provides an optical beam shutter system. Alternatively, as should be obvious to the skilled worker in view of the above description, the optical analyzer 505 may be omitted and the exit optical beam will then have an optical polarization direction which is spatially oriented at an angle of 0 or depending upon the throw of the switch 602; thereby, the optical system shown in FIGS. S and 6 (without the analyzer 565) can be used as a controllable optical polarization rotator, useful for utilization for example by doubly refracting prisms in digital light deflection systems as known in the art.

Although the transparent electrodes shown in FIGS. 5' and 6 are shown as slightly spaced apart, these electrodes can be made in registry at their edges by overlapping thern, but prevented from mutual contact by transparent electrically insulating layers therebetween.

Althoughthe invention has been described in detail in terms of specific embodiments, various modifications can be made by the skilled worker without departing from the scope of the invention. In particular, various other ferroelectric crystal materials can be used, such as terbium molybdate; and the boundary of the ferroelectric domains need not touch any physical boundary of the crystal.

What is claimed is:

l. A device which comprises:

a. a ferroelectric plate capable of supporting a polarized domain, the boundary of which can be displaced in the plate in response to electric fields; o. a first electrode located on a first surface portion of the plate of sufiicient lateral extent and sufficiently proximate to an edge of the plate that the first electrode is substantially coextensive with the boundary of the domain in response to a first voltage applied to the first electrode; and Y a second electrode located on a second surface portion of the plate in sufficient proximity to the first electrode that the domain expands laterally in response to a second voltage applied to the second electrode so that the boundary of the domain becomes substantially coextensive with the projection in a geometric plane in the plate of the outer contour of the first and second electrodes.

2. An optical display device including:

a. the device recited in claim 1; and

b. optical means to detect the domain.

A device according to claim 2 in which the electrodes are both transparent to the optical radiation in the optical means.

4. The device recited in claim 2 in which the optical means include an optical polarizer located in the path of an optical beam exiting'from the plate.

5. A device which comprises:

a. a ferroelectric plate capable of supporting a polarized domain, the boundary of which can be displaced in the plate in response to electric fields; an array of electrodeson a surface portion of the plate including a second electrode as next neighbor to a first electrode and a third electrode as next neighbor to the second electrode; and c. means for applying voltage pulses to the array of electrodes in a sequence consisting of a first pulse 7 8 of one polarity to the first electrode, a second propagate throughallthe plates; pulse of opposite polarity to the third electrode, a b. at least two transparent electrodes located on third pulse of the one polarity to the second elecmajor surfaces of each of the plates; and Ode, a fourth Pulse of pp P y to the c. voltage means connected to the electrodes suffifirst electrode, a fifth pulse of the one polarity to the third electrode, and a sixth pulse of opposite polarity to the second electrode. 6. The device recited in claim 5 in which the first, second, and third electrodes are transparent to an opticient to move the boundaries of the domains in response to the voltage applied to the electrodes such that each domain is extended from coextension with one electrode to coextension with two Cal beam electrodes, so that the relative phase retardation of '7 Apparatus which com rises, 10 perpendicular polarization components of the a the device recitedin claim and beam of radiation propagating through the three b. a source of the optical beam, arranged to direct plites is changed by a predetermined phase by the the beam so th t t tageu se d, and s; f g i through the first "9. The device recited 1n claim 8 in which the plates 8, A d i hi comprises: have a thickness such that the predetermined phase is a. first, second, and third ferroelectric plates each of 77/2 or Odd i mljdnplfe therjeof which is bl f supporting polarized demains w. The device recited in claim Q which further inthe boundaries of each of which can be displaced cludes a quarter-wave plate located in the path of the in response to electric fields, the plates arranged 2O beam such that a beam of optical radiation can I 

2. An optical display device including: a. the device recited in claim 1; and b. optical means to detect the domain.
 3. A device according to claim 2 in which the electrodes are both transparent to the optical radiation in the optical means.
 4. The device recited in claim 2 in which the optical means include an optical polarizer located in the path of an optical beam exiting from the plate.
 5. A device which comprises: a. a ferroelectric plate capable of supporting a polarized domain, the boundary of which can be displaced in the plate in response to electric fields; b. an array of electrodes on a surface portion of the plate including a second electrode as next neighbor to a first electrode and a third electrode as next neighbor to the second electrode; and c. means for applying voltage pulses to the array of electrodes in a sequence consisting of a first pulse of one polarity to the first electrode, a second pulse of opposite polarity to the third electrode, a third pulse of the one polarity to the second electrode, a fourth pulse of opposite polarity to the first electrode, a fifth pulse of the one polarity to the third electrode, and a sixth pulse of opposite polarity to the second electrode.
 6. The device recited in claim 5 in which the first, second, and third electrodes are transparent to an optical beam.
 7. Apparatus which comprises: a. the device recited in claim 6; and b. a source of the optical beam, arranged to direct the beam so that it propagates through the first, second, and third electrodes.
 8. A device which comprises: a. first, second, and third ferroelectric plates each of which is capable of supporting polarized domains, the boundaries of each of which can be displaced in response to electric fields, the plates arranged such that a beam of optical radiation can propagate through all the plates; b. at least two transparent electrodes located on major surfaces of each of the plates; and c. voltage means connected to the electrodes sufficient to move the boundaries of the domains in response to the voltage applied to the electrodes such that each domain is extended from coextension with one electrode to coextension with two electrodes, so that the relative phase retardation of perpendicular polarization components of the beam of radiation propagating through the three plates is changed by a predetermined phase by the voltage.
 9. The device recited in claim 8 in which the plates have a thickness such that the predetermined phase is pi /2 or odd integral multiple thereof.
 10. The device recited in claim 9 which further includes a quarter-wave plate located in the path of the beam. 